Expression Patterns of vnd Gene in Larval and Adult Stages of Drosophila Melanogaster

The Drosophila ventral nervous system defective (vnd) gene encodes a homeodomain transcription factor which initiates neural development in the ventral portion of neuroectoderm. The functions of vnd in regulating neuroblast (NB) formation during embryonic nervous system development have been extensively studied, however, little is known about its roles during the larval and adult development. The core promoter region corresponding to the -5.3 to -2.8 kb from the 5'-flanking region of the vnd gene contains strong enhancers required for NB formation in Drosophila embryos. This region can be divided into two fragments, a distal element containing approximately 1.3 kb DNA fragment (-5.3 to -4.0 kb) and a proximal element carrying about 1.2 kb fragment (-4.0 to -2.8 kb). To study expression pattern of vnd gene after embryonic stage, transgenic lines carrying either a distal or a proximal element were generated, and the expression pattern of the vnd gene was observed by the expression of a green fluorescence protein (GFP) reporter gene. The transformants carrying either a distal or a proximal element show GFP expression in salivary gland, gut epidermis tissue, and testis during larval and adult stages. GFP expression was also observed in the larval brain from the transgenic line containing the proximal element; however, no expression was detected in the adult brain. To identify an enhancer region responsible for the vnd expression, the transgenic lines carrying various deletions within the promoter region were generated. The results show that in the distal element, D4 motif (-4073 to -4051 bp) is essential for vnd expression, and in the proximal element, both 660 bp from the 5' end and 172 bp from the 3' end are Indispensable for vnd expression after embryonic stages. These results suggest that vnd may function throughout Drosophila life span beyond embryogenesis.